Apparatus known as “document production apparatus” are generally configured to process one or more sheets of media (such as paper) to thereby form the media into a finished document. Some document processing apparatus can bind a plurality of sheets into a single document. Other document production apparatus can include a sheet folding device that can fold a sheet of media, such as paper, into a bi-fold, tri-fold, or other multi-folded pamphlet. For example, FIG. 1 depicts a tri-fold pamphlet 10 formed from a single sheet of media “M”. The sheet “M” is folded along a first fold line 18 which segregates the sheet “M” into portions 12 and 14. The sheet “M” is further folded along a second fold line 20 which further segregates the sheet “M” into portions 14 and 16. Document processing apparatus having sheet-folding capability are known in the art. (See, for example, U.S. Pat. No. 6,132,352, incorporated herein by reference.)
Also known are document production apparatus which incorporate a trimming or cutting device which can cut or trim media to a desired size. (See, for example, U.S. Pat. Nos. 5,527,567 and 5,708,345, which are both incorporated herein by reference.) Such trimming and cutting devices allow media to be provided from a continuous roll of media, and also allow a document to be trimmed to a desired size after imaging.
Some prior art apparatus used to fold a sheet of media into a multi-fold pamphlet typically incorporate a pinch bar or pinch roller (a “pinch device”) which urges a portion of the sheet, along which a fold is to be formed, towards a pair of counter-rotating fold-forming rollers. For purposes of the following discussion, I will define the line along which a fold is to be formed in a sheet of media as the “intended fold line”, and the line along which the actual fold is formed as the “fold line”. The counter-rotating rollers, which are preferably in contact with one another and are aligned along parallel axes, then engage the sheet in the area of the intended fold line. The area in which the counter-rotating rollers (the “fold rollers”) engage the sheet is known as the “nip”. As the sheet passes through the fold rollers, the sheet is folded along the fold line. The sheet can then be passed through another set of fold rollers, or passed back though the original set of fold rollers, to form additional folds in the sheet. This is graphically demonstrated in FIG. 2, which shows a side elevation view of a sheet of media “M” being folded into leaves 31 and 33. The actual fold line will generally be located in the area 38. A pinch roller 30 moves in direction “A” to move the fold area 38 towards the nip 36 and into the counter-rotating fold rollers 32 and 34. The fold rollers 32 and 34 grasp the sheet “M” as it is urged into the rollers, and thereby folds the sheet “M” into a bi-fold sheet.
Such prior art apparatus sheet folding apparatus present several deficiencies. First, the pinch bar does precisely direct the intended fold line towards the nip, but only approximates the position of the intended fold line. This is demonstrated in FIG. 2, where the actual fold line will be formed in the fold area 38, but is not clearly defined in this fold area. As a result, the actual fold can be formed in a slightly different location on the sheet than the desired fold line. In addition to the actual fold line not being coincident with the intended fold line, the actual fold line can also be skewed with respect to the intended fold line. This is demonstrated in FIG. 3, which shows a sheet of media “M” which is intended to be folded into two equal parts along the intended fold line 44, but in fact is folded along the actual fold 42, which is offset at a slight angle to the intended fold line 44. The result it that when the first half 46 of the sheet “M” is folded over the second half 48 of the sheet, the first edge 31 will not align with the second edge 33, providing a visually unattractive pamphlet.
In other prior art sheet folding apparatus, rather than use a pinch bar to move the document into the fold rollers, a stop device is used to stop forward progress of the sheet. Since the sheet is still being fed by feed rollers, the sheet will be caused to buckle and move into the fold rollers. This results in the fold being formed along a rather imprecise line, since the area where the sheet will buckle can vary with the sheet thickness and other variables. Further, the use of a stop device generally limits the thickness of sheet media which can be used to form the folded pamphlet, since relatively thick sheets will tend to crumple rather than buckle.
Another problem occurs when the fold line passes through an image (such as text or graphics) on the sheet of media. In this event, folding the sheet along the fold line can cause small portions of the image in the fold area to separate from the sheet. This problem is particularly noted when the image is formed using a toner which is fused to the sheet to create the image.
A further problem with prior art sheet folding apparatus is that they generally require forward progress of the sheet media to be temporarily halted while the sheet media is moved into the nip of the fold rollers. When the sheets to be folded are being provided from an attached imaging device, this can determine the speed of the imaging device, since the sheet folding device generally will not be able to process sheets of media as quickly as the imaging device. Accordingly, anything which can be done to improved the speed at which sheets of media can be folded by the sheet folding device will generally allow the imaging device to operate closer to its design speed, thus improving the speed of the overall imaging-folding process.
What is needed then is a document processing apparatus which achieves the benefits to be derived from similar prior art devices, but which avoids the shortcomings and detriments individually associated therewith.